Editors' ChoiceCircadian Biology

Biochemical basis of a 24-hour clock

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Sci. Signal.  21 Jul 2015:
Vol. 8, Issue 386, pp. ec200
DOI: 10.1126/scisignal.aad0390

Circadian clocks keep organisms in sync with such daily cycles as illumination, activity, and food availability. The circadian clock in cyanobacteria has the necessary 24-hour period despite its three component proteins having biochemical activities that occur on a much faster time scale. Abe et al. focused on the cyanobacterial clock component KaiC, an adenosine triphosphatase (ATPase) that can autophosphorylate and autodephosphorylate. The slow ATPase activity of KaiC, which is linked to a peptide isomerization, provided the slow kinetics that set the speed of the 24-hour clock. Chang et al. found that another clock component, KaiB, also has slow changes in its protein conformation that help to set the oscillation period of the clock and its signaling output.

J. Abe, T. B. Hiyama, A. Mukaiyama, S. Son, T. Mori, S. Saito, M. Osako, J. Wolanin, E. Yamashita, T. Kondo, S. Akiyama, Atomic-scale origins of slowness in the cyanobacterial circadian clock. Science 349, 312–316 (2015). [Abstract] [Full Text]

Y.-G. Chang, S. E. Cohen, C. Phong, W. K. Myers, Y.-I. Kim, R. Tseng, J. Lin, L. Zhang, J. S. Boyd, Y. Lee, S. Kang, D. Lee, S. Li, R. D. Britt, M. J. Rust, S. S. Golden, A. LiWang, A protein fold switch joins the circadian oscillator to clock output in cyanobacteria. Science 349, 324–328 (2015). [Abstract] [Full Text]